This invention relates generally to internal field activated display sheets and more particularly concerns an internal field activated display sheet which utilizes liquid in a plurality of reservoirs in which the liquid can be moved from each reservoir into an open space and can be moved back into the reservoir by applying an electric field to the liquid.
Typically, a display device, in sheet form, comprises a thin sheet, which has many attributes of a paper document. It looks like paper, has ambient light valve behavior like paper (i.e. the brighter the ambient light, the more easily it may be seen), is flexible like paper, can be carried around like paper, can be written on like paper, can be copied like paper, and has nearly the archival memory of paper.
There have been different approaches to making a field induced display sheet such as U.S. Pat. No. 5,956,005 titled xe2x80x9cElectrocapillary Display Sheet which Utilizes an Applied Electric Field to Move a Liquid Inside the Display Sheetxe2x80x9d, in which the display sheet utilizes three transparent parallel sheets spaced from each other. The medial plane has a plurality of reservoirs, which are filled with a dyed or pigmented ink. Each of the reservoirs has an individually addressable voltage source to create an individual electric field. Ink from a reservoir flows into the space between the medial plane and one of the other two sheets with the application or removal of an electric field.
An alternate approach was disclosed in U.S. Pat. No. 5,717,283 titled xe2x80x9cDisplay Sheet with a Plurality of Hourglass Shaped Capsules Containing Marking Means Responsive to External Fieldsxe2x80x9d, in which the display sheet contains a plurality of hourglass shaped capsules for each pixel of an image. Each hourglass shaped capsule contains ink in one of its chambers. With the application of an external electric field, ink is moved from one chamber to the other in each hourglass shaped capsule to display an image. Visibility of the ink is otherwise blocked by an opaque medial plane.
Although these approaches, utilizing a standard vertical electric field, are useful, it is desirable to improve on their performance. Accordingly, it is an object of this invention to provide a means for more effectively moving material within electric paper pixels than is possible with a standard vertical electric field.
Briefly stated, and in accordance with one aspect of the present invention, there is provided an internal activated display sheet including a medial plane disposed between a first and second reservoir. Apertures in the medial plane permit communication between the first and second reservoirs. At least one of the reservoirs is filled with a liquid responsive to an internal peristaltic field developed within the medial plane, which includes a plurality of conductors. Applying an internal field across selected apertures in the medial plane causes liquid to move from one reservoir to the other.
In an alternate aspect of the invention there is provided a method for activating a display sheet having a first non-conductive sheet, a plurality of first reservoirs, a plurality of second reservoirs located beneath the first reservoirs, a medial plane containing conductive means interposed between the first and second reservoirs. Apertures in the medial plane permit communication between the first and second reservoirs. At least one of the reservoirs is filled with a liquid means. A peristaltically driven internal field within the medial plane pumps the liquid means from at lease one of the filled reservoirs into one of the reservoirs not containing the liquid means.